The present invention relates to a touch pad and, more specifically, to a touch pad, based on piezoelectric effect, that employs a piezo film, is fabricated thin on, but not limited to, metal, exactly and stably recognizes various touch patterns a user executes such as long key, multi key, slide key, etc. and significantly improves the level of security.
Touch-sensitive switch technology that has been thus far developed includes a (reflective mode ultrasonic) touch-sensitive switch comprising: a substrate having a touch region thereon; a piezoelectric element that has electrodes; drive means that apply a drive signal to the electrodes; detection means that provide a detection signal derived from the drive signals; and discriminating means that provide an output signal. (Refer to U.S. Pat. No. 5,673,041)
Such a touch-sensitive switch has a first surface and a second surface that are opposed and parallel to each other, wherein the first surface has a substrate having a touch region; and a piezoelectric element having first and second generally planar and parallel opposed surfaces and an electrode on each of the piezoelectric element surfaces, wherein the piezoelectric element is secured, from the touch region, across the substrate, in parallel with the second surface of the substrate.
In addition, such a touch-sensitive switch has drive means that are coupled to the electrodes to apply a drive signal to the electrodes; detection means that are coupled to the electrodes to provide a detection signal derived from the drive signal; and discriminating means that are equipped for receiving the detection signal from the detection means in order to evaluate the detection signal and provide an output signal that indicates a finger touch to the touch region.
Based on such a configuration, a frequency-modulated drive signal is applied to the piezoelectric element that is mounted on the substrate opposed to the touch region, the piezoelectric element converts the signal to an amplitude-modulated signal and the amplitude-modulated signal is demodulated, wherein the amplitude of the demodulated signal varies according to whether a finger touches to the touch region.
Therefore, the touch region does not easily get damaged, the reliability of a touch increases to a certain extent and the sensibility of the sensor does not decrease to a large extent even if the force of a touch gradually increases. On the other hand, the severe disadvantage of ultrasonic touch-sensitive switches according to existing technology has still been maintained per se in that those switches are vulnerable to touch errors brought about by foreign substances such as water or ketchup.
Meanwhile, simple piezoelectric devices are vulnerable to external impacts or vibration. Piezoelectric devices especially for touch recognition may not produce an adequate amount of output if the plate, such as metal, that is equipped with touch keys is thick or the clearance between the touch keys is narrow, which fails to guarantee exact and stable touches of users.
In addition, those piezoelectric touch devices that utilize the piezo effect existing technology provides can neither be directly applied, without an additional process, to metal, advanced materials, etc. nor produce an appropriate value of the electric displacement of the piezoelectric devices when a touch object is slowly detouched even with a touch input on the metal plate, etc. that is equipped with touch keys.
Here, another drawback is derived in that the devices may not safely recognize such behaviors as long key input that maintains the state of a key input for a certain period, multi key input that simultaneously inputs multiple keys and wheel slide touch input that is, as a drag touch, the touch object is detouched after a short period.
Therefore, security keys users can specify such as password are very restricted in terms of their species and it is practically hard to expect a high degree of security because there is a limit to recognition of long key input and multi key input in applying a touch device using the piezo effect to a metal plate, etc.
Furthermore, those piezoelectric touch devices using the piezo effect of existing technology that employ ceramic piezoelectric elements cannot be fabricated considerably thin and are hard to be achieved in smartphones, etc.